1. Field of Invention
The present invention relates to a rotary labelling machine of the type comprising a carrousel supporting a plurality of bottle-holding plates along the periphery thereof, in which the carrousel can be pivotally driven by a carrousel motor in order to be able to place each individual plate of the carrousel at one or more labelling stations arranged about the carrousel, and in which each bottle-holding plate is associated with a drive motor suitable to rotate the plate about the axis thereof in order to be able to place the bottle, or generally the container being supported by the plate, in the angular positions required for applying the label.
2. Description of the Prior Art
In order to achieve a satisfactory labelling, for example of containers different from one another, containers having a non-cylindrical shape, and containers having, in addition to the label, further ornamental or technical accessories requiring the label to be placed in dependency from the position of the further accessory, labelling machines are provided with command and control means driving the drive motors of the plates, such that a preset movement and positioning is imposed to each plate as a function of the angular position of the carrousel in order to properly orientate the containers to be labelled when they are conveyed to the labelling stations.
Electric motors have been proposed for driving the bottle-holding plates, such as direct current, alternate current or three-phase motors. These motors can be of the synchronous, asynchronous or stepping types. These electric motors are connected to the bottle-holding plate, with or without a drive mechanism being interposed therebetween.
A known solution provides that said command and control means for the drive motors comprise a controller (usually a computer), which is connected by means of suitable control lines (usually electrical wires) on the one side with an angular position sensor of the carrousel, and on the other side, with drive motors or power stages, which are, in turn, connected to the drive motors. The controller is programmed to process signals received from the angular position sensor and to generate response signals that command the drive motors or the power stages of the drive motors in order to impose the desired movement to the plate.
Since each individual plate, and thus each individual drive motor of a carrousel that can indicatively contain fifteen to sixty plates follows a different movement profile from that of the other motors and requires its own control line, or in other words, its own channel of bidirectional communication with the controller, the number of electrical connections is very high, thus resulting in a complicated system difficult to be managed.
In order to reduce the amount of wiring, while maintaining the same data flow between the controller and the power stages of the motors, the use of a communication bus has been suggested, which is suitable to receive a signal flow from the controller and distribute it to each drive motor in a selective manner.
As all the required information (movement profile and positioning of each motor) and all the processing operations (e.g., the calculation of the angular position and/or angular speed and/or angular acceleration and/or relative electrical power quantities of the motor) reside in the controller, a high performance of the communication bus is required in order to sort and distribute, in a sequential manner, the control signals to each one of the number of motors in a very short time (in the order of milliseconds). Furthermore, since the motors are placed in a rotating part of the labelling machine, the transmission of electric power and control signals from the controller to the motors is usually carried out via sliding contact rotary commutators.
The huge amount of data to be exchanged by means of the bus and sliding contacts requires that high performing communications buses are used, which besides being expensive, are particularly sensitive to interference and thus not much suitable in this field.
The object of the present invention is thus to provide a labelling machine having command and control means for the drive motors such as to obviate to the drawbacks cited with reference to the prior art.
This and other objects are achieved by a rotary labelling machine comprising:
a carrousel to be pivotally driven by a carrousel motor;
    a plurality of container stations supported by said carrousel, in which each container station comprises a container-holding plate and a plate motor suitable to rotate the plate about its own axis,    control means suitable to control the movement of the plates as a function of the movement of the carrousel,    wherein said control means comprise:    carrousel sensor means suitable to detect the movement of the carrousel and generate a reference signal representative of a movement parameter of the carrousel, such as the direction of rotation and/or the angular position and/or the instantaneous angular speed of the carrousel;a plurality of local control units, each being connected to one of the plate motors, respectively, and being arranged either in the vicinity of the plate motor or within the housing thereof, and configured to receive and process said reference signal and generate a specific control signal for said motor as a function of the reference signal;    signal propagation means being connected to the carrousel sensor means and to each of the local control units and configured such that, when the labelling machine is working, they receive the reference signal from the carrousel sensor means and propagate said reference signal to each of the local control units.
A dramatic reduction in the amount of transmitted data is obtained, due to the provision of local control units generating the control signal specific for the respective plate motor and due to the transmission of the reference signal (i.e. only one signal/instant) which is the same for all the plate motors. This results in a considerable increase in the transmission speed, with the performance of the signal propagation means remaining unchanged, and allows using a robust communication bus insensitive to interferences. As the specific control signals are calculated locally, and a plurality of local calculation processes are driven by an individual “poor” reference signal that is transmitted within the network and is valid for all the motors, the number of container stations can be increased per each carrousel, in addition to ensuring the signal solidity. An even higher performance can be also achieved in terms of control of the plate movement than so far achievable by means of a mechanical cam control, without however renounce the advantages of electronic controls, such as versatility and adaptability of the system to various types of containers and labels.